Hydraulic tank with wall stressing means

ABSTRACT

A rectangular tank for a heavy duty hydraulic system which may produce pressure variations within the tank. Stiffeners are bonded to the outer surfaces of the walls; and in addition at least one internal tie rod extends between opposed mounting members on two opposite walls and has threads of opposite hand at its end portions engaged with corresponding threads in the mounting members so that rotation of the tie rod in one direction pushes the opposite walls apart at the mounting members while rotation of the tie rod in the other direction draws the walls toward one another at said mounting members, thus prestressing the walls to any desired extent.

United States Patent [1 1 McMillan May 13, 1975 HYDRAULIC TANK WITH WALL STRESSING MEANS [75] Inventor: William D. McMillan, Joliet, 111. [73] Assignee: Caterpillar Tractor Co., Peoria, 111.

[22] Filed: Apr. 19, 1974 [21] Appl. No.: 462,333

FOREIGN PATENTS OR APPLICATIONS 567,936 3/1945 United Kingdom 220/71 Primary Examiner-George E. Lowrance ABSTRACT A rectangular tank for a heavy duty hydraulic system which may produce pressure variations within the tank. Stiffeners are bonded to the outer surfaces of the walls; and in addition at least one internal tie rod extends between opposed mounting members on two opposite walls and has threads of opposite hand at its end portions engaged with corresponding threads in the mounting members so that rotation of the tie rod in one direction pushes the opposite walls apart at the mounting members while rotation of the tie rod in the other direction draws the walls toward one another at said mounting members, thus prestressing the walls to any desired extent.

7 Claims, 2 Drawing Figures [52] US. Cl. 220/71 [51] Int. Cl 865d 7/44 [58] Field of Search 220/71, 5 A, 3, 1 B

[56] References Cited UNITED STATES PATENTS 1,686,931 10/1928 Russell 220/71 1,757,923 5/1930 Russell 220/71 1,895,747 1/1933 Beldimanu 220/71 3,062,402 11/1962 Farrell 220/71 3,451,452 6/1969 Marshall 220/71 3,712,139 1/1973 Harvey 220/71 1 1 }i 21 f l 21 1 t 25 J HYDRAULIC TANK WITH WALL STRESSING MEANS BACKGROUND OF THE INVENTION Heavy duty hydraulic systems of the type used in present day earth moving machinery require a large size hydraulic reservoir, both because of the large number of hydraulic functions available on such machines today, and because of the size of the machines. A large size reservoir has tank walls with large surface areas exposed to fluid pressure, resulting in greater likelihood of tank wall deformation during operation of the machinery. Although such systems are designed to operate at substantially zero tank pressure, it has been observed that some of the complex, heavy duty hydraulic systems now used on earth moving equipment can cause variations in tank pressure between +20 and 3 psi.

Although it is theoretically possible to meet the problem of tank pressure variations by building the tanks with heavier side walls, this is not a practical solution because of the relatively high cost of heavy gauge steel, the comparatively higher cost of fabricating a tank from heavy gauge steel, and the additional weight represented by the tank. It has been found that a much more satisfactory solution is to provide stiffeners on the tank walls which may conveniently take the form of externally mounted channel members which have their legs bonded to the tank walls and their webs in spaced relationship to the walls. Even with such stiffeners, a generally rectangular tank for 1 gallons of hydraulic fluid (180 gallons capacity) which is fabricated of 1 4 inch steel and has major front and rear walls 51 V8 high X 21 inches wide, with a depth of 38% inches, can have a total wall deflection at psi which exceeds 0.75 inches from front to rear of the tank.

In addition to the foregoing problem of wall deflection, manufacturing tolerances for the separate piece parts which comprise the five closed sides of the tank can result in a tolerance buildup which can be accommodated by adjustable tie rods.

SUMMARY OF THE INVENTION In accordance with the present invention, the major walls of a tank, which are usually the front and rear walls, are connected by tie rods which have threads of opposite hand at their two ends that are engaged with correspondingly threaded bores in opposed mounting members on the major walls. Thus, rotation of the tie rod in one direction moves the major tank walls apart at the mounting members, while rotation in the other direction draws the major tank walls toward one another at said mounting membersf A hex nut welded onto the tie rod near one end accommodates a wrench to facilitate rod adjustment.

The structural strength of the assembly is enhanced by positioning the opposed mounting members in line with a pair of external stiffening members.

The mounting members are secured to the major tank walls by screws which impale holes in the tank walls and are threaded into blind bores in the mounting members, and annular channels in the faces of the mounting members surrounding the blind bores mount O-rings which provide seals surrounding the holes in the tank walls.

Access to the mounting screws requires that the channel-like stiffeners have apertures aligned with the holes in the tank wall, and short sleeves are bonded to the periphery of the apertures and abut the tank wall surrounding the heads of the mounting screws. This arrangement further increases the structural integrity of the tank.

A tank of the dimensions heretofore described, and provided with substantially the arrangement of stiffeners illustrated in the drawings, was tested for deflection at 20 psi, which is the maximum encountered in present day tanks because they are equipped with pressure relief valves set at that level. Such a tank had a deflection of 0.773 inches across the front and rear walls.

When one tie rod and mounting means was installed in the tank the deflection at the same pressure was reduced to 0.522 inches. When two tie bars and mounting members of the present type were installed the deflection was reduced to 0.164 inches, which is considered to be nominal.

THE. DRAWINGS FIG. 1 is a front elevational view of a tank embodying the invention; and

FIG. 2 is a fragmentary secctional view on an enlarged scale taken substantially as indicated along the line 11-11 of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. I, a hydraulic tank, indicated generally at 10, is of generally rectangular shape so that it has major front and rear walls 11 and 12, respectively, connected by a right side wall 13, a left side wall 14 and a bottom wall 15. The tank has an open top and a removable closure 16 which is secured to a flange 17 by a plurality of bolts 18. An oil filler spout 19 is fixed to the closure 16 and extends into the tank, and a removable cap 20 on the filler spout seals the tank.

A plurality of external horizontal stiffeners 21 are welded to the major walls 11 and 12; and similar horizontal stiffeners 21 may also be welded to the side walls 13 and 14. A plurality of vertical stiffeners 22 are welded to the major walls 11 and 12 and are connected to bottom wall stiffeners 23. The horizontal stiffeners 21 are interrupted by the vertical stiffeners 22 on both the major walls; and at their points of intersection the horizontal stiffeners overlap the vertical stiffeners and are welded to them. All the stiffeners are channel-like, with legs such as the legs 24 welded to the tank walls and webs such as the webs 25 spaced from the tank walls. A mounting flange and suction port 26 provides a flow path from the tank to the hydraulic system.

Adjustable wall stressing means, indicated generally at 30, includes a front mounting member 31, a rear mounting member 32, and a tie rod 33. The mounting members 31 and 32 are secured, respectively, to the front wall 11 and to the rear wall 12 by a plurality of screws 34 each of which impales a hole 35 in the wall 11 or 12 and screws into a threaded blind bore 36 to secure the mounting members 31 and 32 in abutting relationship with the walls 11 and 12. Washers 37 are sandwiched between the walls and screw heads 34a of the mounting screws 34.

An annular groove 38 surrounds each of the blind bores 36, and O-rings 39 in the grooves seal the mounting members 31 and 32 to the tank walls 11 and 12.

The webs 25 of the stiffeners 21 which contain a wall stressing means 30 are provided with apertures 40 which give access to the screws 34 from the outside of the tank. A sleeve 41 in each aperture 40 is welded to the web 25 at one end and is in abutting relationship with the wall 11 or 12, as the case may be, at the opposite end. The sleeves 41 provide support for the stiffeners 21 and reinforce the walls 1 l and 12 about the holes Although the front mounting member 31 and the rear mounting-member 32 are identical in configuration, the former contains a centrally disposed righthand threaded bore 42 while the latter contains a centrally disposed lefthand threaded bore 43. The tie rod 33 has threads 33a and 33b of opposite hand at its end portion. Thus, clockwise (as seen in FIG. 1) rotation of the tie rod draws the mounting members 31 and 32 and the walls 11 and 12 toward one another, whereas counterclockwise rotation of the tie rod pushes the mounting members 31 and 32 and the walls 11 and 12 apart. It can be seen that, within limits, varying the distance between the front and rear walls 11 and 12 can compensate for tolerance stackup. Further, prestressing of the walls by the means 30 restricts deflection of the walls due to pressure variations within the tank. .1

The wall stressing means is installed in the interior of the tank by access through the open top after the tank has been assembled. Initially the mounting members 31 and 32 are screwed onto the ends of the tie rod 33 far enough that they do not project past its ends, and the assembly is inserted into the tank. The mounting members are then screwed out until they abut the front and rear walls, and they are fastened to the walls by inserting the screws 34 through the walls. The tie rod 33 is then rotated to prestress the walls inwardly under a predetermined torque. While the torque may vary over a considerable range, a satisfactory torque loading is one which will permit substantially zero wall deflection when there is a pressure of psi in the tank.

Rotation of the tie rod 33 is facilitated by placing a nut 44 on the thread near one rod end and welding it in place to accommodate a wrench.

The foregoing detailed description is given for clearness of understanding only and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

I claim:

1. In a tank for a heavy duty hydraulic system which may produce pressure variations within the tank, said tank having generally parallel major walls connected by side walls and a bottom wall, an open top, and a removable closure for the open top, and wall stiffeners bonded to at least the major walls, adjustable wall stressing means comprising, in combination:

a pair of mounting members secured to opposed areas on the inner surfaces of the major walls, said mounting members having aligned facing bores and being manually accessible through the open top of the tank;

a tie rod which has its end portions rotatably interengaged within said bores;

and screw thread means functionally related to said tie rod so that rotation of the tie rod in one direction moves said major walls apart at the mounting members and rotation of the tie rod in the opposite direction draws the major walls toward one another at said mounting members through the interengagement of the tie rod in the bores.

2. The combination of claim 1 in which the screw thread means comprises an internal screw thread in one of said bores, and a screw thread on an end portion of the tie rod which is engaged with said internal screw thread.

3. The combination of claim 1 in which the screw thread means comprises internal screw threads in both said bores which are of opposite hand to one another, and screw threads of opposite hand on the end portions of the tie rod each of which is engaged with one of said internal screw threads.

4. The combination of claim 1 in which each major wall has adjacent holes, each mounting member has threaded blind bores aligned with said holes, headed screws impale the holes and engage said blind bores to secure the mounting member to the wall, and sealing means surrounds each hole.

5. The combination of claim 4 in which each mounting member has an annular groove surrounding each blind bore, and the sealing means comprises an O-ring seated in the groove.

,6. The combination of claim 4 in which the wall stiffeners comprise channel-like members having legs bonded to the outer surfaces of the major walls in alignment with one another and webs in spaced relationship to the major walls, apertures in said webs aligned with the adjacent holes in the tank walls, and a sleeve member bonded to each stiffener web surrounding each aperture and abutting the wall surrounding the hole, said apertures and sleeve members being larger than the heads of the screws which secure the mounting members to the walls.

7. In a tank for a heavy duty hydraulic system which may produce pressure variations within the tank, said tank having generally parallel major walls connected by side walls and a bottom wall, an open top, and a removable closure for the open top, and wall stiffeners bonded to at least the major walls, adjustable wall stressing means comprising, in combination:

a pair of mounting members secured to opposed areas on the inner surfaces of the major walls, said mounting members being manually accessible through the open top of the tank;

and tie rod means interconnecting said mounting members, said tie rod means having end portions provided with threads of opposite hand which are engaged with complementary threads so that rela-- tive rotation between said end portions and said complementary threads produces relative motion between the mounting members. 

1. In a tank for a heavy duty hydraulic system which may produce pressure variations within the tank, said tank having generally parallel major walls connected by side walls and a bottom wall, an open top, and a removable closure for the open top, and wall stiffeners bonded to at least the major walls, adjustable wall stressing means comprising, in combination: a pair of mounting members secured to opposed areas on the inner surfaces of the major walls, said mounting members having aligned facing bores and being manually accessible through the open top of the tank; a tie rod which has its end portions rotatably interengaged within said bores; and screw thread means functionally related to said tie rod so that rotation of the tie rod in one direction moves said major walls apart at the mounting members and rotation of the tie rod in the opposite direction draws the major walls toward one another at said mounting members through the interengagement of the tie rod in the bores.
 2. The combination of claim 1 in which the screw thread means comprises an internal screw thread in one of said bores, and a screw thread on an end portion of the tie rod which is engaged with said internal screw thread.
 3. The combination of claim 1 in which the screw thread means comprises internal screw threads in both said bores which are of opposite hand to one another, and screw threads of opposite hand on the end portions of the tie rod each of which is engaged with one of said internal screw threads.
 4. The combination of claim 1 in which each major wall has adjacent holes, each mounting member has threaded blind bores aligned with said holes, headed screws impale the holes and engage said blind bores to secure the mounting member to the wall, and sealing means surrounds each hole.
 5. The combination of claim 4 in which each mounting member has an annular groove surrounding each blind bore, and the sealIng means comprises an O-ring seated in the groove.
 6. The combination of claim 4 in which the wall stiffeners comprise channel-like members having legs bonded to the outer surfaces of the major walls in alignment with one another and webs in spaced relationship to the major walls, apertures in said webs aligned with the adjacent holes in the tank walls, and a sleeve member bonded to each stiffener web surrounding each aperture and abutting the wall surrounding the hole, said apertures and sleeve members being larger than the heads of the screws which secure the mounting members to the walls.
 7. In a tank for a heavy duty hydraulic system which may produce pressure variations within the tank, said tank having generally parallel major walls connected by side walls and a bottom wall, an open top, and a removable closure for the open top, and wall stiffeners bonded to at least the major walls, adjustable wall stressing means comprising, in combination: a pair of mounting members secured to opposed areas on the inner surfaces of the major walls, said mounting members being manually accessible through the open top of the tank; and tie rod means interconnecting said mounting members, said tie rod means having end portions provided with threads of opposite hand which are engaged with complementary threads so that relative rotation between said end portions and said complementary threads produces relative motion between the mounting members. 